Back to EveryPatent.com
United States Patent |
5,607,778
|
Padden
|
March 4, 1997
|
Method of manufacturing a porous metal mat
Abstract
Multiple layers of expanded electrically conductive metal foil are stacked,
some of the layers are expanded and some are flattened. After the stack of
layers is formed, it is compressed and the layers are bonded together to
form a semi-rigid electrically conductive porous metal mat.
Inventors:
|
Padden; James B. (Kernersville, NC)
|
Assignee:
|
Purolator Products Company (Tulsa, OK)
|
Appl. No.:
|
504613 |
Filed:
|
July 20, 1995 |
Current U.S. Class: |
428/613; 228/190 |
Intern'l Class: |
B32B 003/24; B23K 101/22 |
Field of Search: |
428/596,613,636
228/190
204/284
|
References Cited
U.S. Patent Documents
1626774 | May., 1927 | Allan | 204/284.
|
2256000 | Sep., 1941 | McNeil | 228/190.
|
2275194 | Mar., 1942 | Sizelove | 204/284.
|
3630312 | Dec., 1971 | Woodward | 181/33.
|
3671415 | Jun., 1972 | King et al. | 204/284.
|
3676315 | Jul., 1972 | Goens et al. | 204/284.
|
3944505 | Mar., 1976 | LaCroix | 252/466.
|
4044218 | Aug., 1977 | Olson et al. | 219/91.
|
4359181 | Nov., 1982 | Chisholm | 228/183.
|
4401530 | Aug., 1983 | Clere | 204/98.
|
4460441 | Jul., 1984 | Domning | 204/284.
|
4605487 | Aug., 1986 | Shiragami et al. | 204/258.
|
5041196 | Aug., 1991 | Cawlfield et al. | 204/101.
|
5137607 | Aug., 1992 | Anderson et al. | 204/59.
|
5137634 | Aug., 1992 | Butler et al. | 210/490.
|
5215943 | Jun., 1993 | Anderson et al. | 501/12.
|
5227342 | Jul., 1993 | Anderson et al. | 501/12.
|
5230780 | Jul., 1993 | Carlson et al. | 204/98.
|
5308454 | May., 1994 | Anderson | 204/59.
|
5340455 | Aug., 1994 | Kroon et al. | 204/196.
|
Primary Examiner: Zimmerman; John
Attorney, Agent or Firm: Tassone; Joseph V.
Claims
What is claimed:
1. A method of manufacture a porous metal mat comprising the steps of:
forming in overlapping relationship a stack of multiple layers of expanded
electrically conductive metal foil to provide an assembly in which some of
the layers are as expanded and some of the layers are flattened after
expansion; and
bonding the assembly of stacked layers to form a mat.
2. The method of claim 1 in which as expanded and flattened layers are
alternated.
3. The method of claim 1 in which said layers are formed of expanded
titanium metal foil.
4. The method of claim 1 in which said layers are of thickness of about
0.005 inches as expanded and of thickness of about 0.004 inches when
flattened.
5. A method according to claim 1 in which said step of bonding the stacked
layers is comprised of stapling, spot welding, riveting, brazing or
diffusion bonding.
6. The method according to claim 4 in which said assembly as bonded is of
thickness of about 0.125 inches to 0.25 inches.
7. A semi-rigid electrically conductive porous mat comprising:
a bonded stack formed of multiple layers of electrically conductive
expanded metal foil in which some of the layers are as expanded and some
are flattened.
8. A semi-rigid electrically conductive porous mat according to claim 7
wherein said as expanded and said flattened layers are alternated.
9. A semi-rigid electrically conductive porous mat according to claim 7 in
which said layers are formed of expanded titanium foil.
10. A semi-rigid electrically conductive porous mat according to claim 7 in
which each said expanded layer as expanded is about 0.005 inches thick and
each said expanded layer as flattened is about 0.004 inches thick.
11. A semi-rigid electrically conductive porous mat according to claim 7 in
which said stack is mechanically bonded.
12. A semi-rigid electrically conductive mat according to claim 7 in which
said stack is bonded by brazing.
13. A semi-rigid electrically conductive mat according to claim 7 in which
said stack is diffusion bonded.
14. A semi-rigid electrically conductive mat according to claim 10 in which
said mat is of thickness of about 0.125 inches to 0.25 inches.
15. A method of manufacturing a porous titanium electrically conductive
metal electrode comprising:
stacking multiple layers of expanded metal foil to form an assembly in
which layers as expanded are alternated with layers of metal foil that are
flattened prior to stacking; and
bonding the assembly of stacked layers into an integral electrode forming
mat.
16. A method of claim 15 in which the layers of expanded metal foil are
each about 0.005 inches as expanded and about 0.004 inches as flattened.
17. The method of claim 15 in which said assembly is diffusion bonded.
18. The method according to claim 16 in which said assembly as bonded is of
thickness of about 0.125 inches to 0.25 inches.
Description
CROSS-REFERENCE TO PENDING APPLICATIONS
This application is not related to any pending United States or foreign
patent application.
CROSS-REFERENCE TO MICROFICHE APPENDIX
This application is not related to any microfiche appendix.
BRIEF SUMMARY OF THE INVENTION
A method of manufacturing a porous metal mat is described. The method
includes forming, in overlapping relationship, a multi-layer stack of
expanded electrically conductive metal foil in which some of the layers of
foil are as expanded and others of the layers are flattened after being
expanded, to provide a stacked assembly. The stacked assembly is then
compressed and bonded to form a semi-rigid electrically conductive mat.
Expanded metal foil is formed from a unitary thin, flat foil sheet. Slits
are cut in the sheet and the foil is stretched, that is, "expanded". The
typical expanded metal foil has diamond-shaped openings as a result of the
expansion. The expanded foil is in the form of connected filaments
outlining the diamond-shaped openings.
When foil is expanded it typically has an uncompressed thickness that is
greater than the foil itself. That is, in the expansion process, typically
the metal strands forming the expanded foil are tilted slightly relative
to the plane of the foil so that the expanded metal foil is somewhat
thicker than the flat foil of which the expanded foil is manufactured.
To manufacturer a porous metal mat according to the present invention, some
of the expanded metal foils (such as 50%) are flattened by a press or by
passing them between rollers to return the expanded metal foil to
approximately the same thickness of the foil prior to expansion. In the
preferred arrangement, a mat is manufactured by stacking the expanded
metal foils in alternate layers, that is, in which a first layer is of the
foil as expanded that has a thickness slightly greater than the normal
foil thickness caused as a result of the expansion followed by a layer of
expanded metal foil that has been flattened, and the sequence repeated
until the desired thickness of the mat is achieved.
In the preferred arrangement, the expanded metal foils are stacked in a way
to avoid alignment of the openings therethrough so as to provide, in the
mat as completed, a high degree of porosity with a minimum of direct flow
paths from one mat surface to the other.
After stacking, the assembly is compressed and bonded to form an integral
semi-rigid electrically conductive mat. Bonding can be mechanical, such as
by stapling or riveting. Bonding can also be achieved by the use of heat,
such as by welding or brazing. A third and a preferred method is diffusion
bonding--a process well known in industry that integrally electrically and
mechanically secures the adjacent sheets to each other, but in a way to
preserve the porosity of the stacked assembly.
Prior art examples of processes that employ electrically conductive porous
metal mats are illustrated and described in the following United States
Patents:
______________________________________
Pat. No. TITLE
______________________________________
5,041,196 Electrochemical Method For Producing
Chlorine Dioxide Solutions
5,137,607 Reactor Vessel Using Metal Oxide
Ceramic Membranes
5,230,780 Electrolyzing Halogen-Containing
Solution In A Membrane Cell
5,308,454 Reactor Process Using Metal Oxide
Ceramic Membranes
5,340,455 Cathodic Protection System For Above-
Ground Storage Tank Bottoms and
Method Of Installing
______________________________________
Of these references, U.S. Pat. No. 5,041,196 is the best example of the use
of a porous electrically conductive metal mat.
Others have suggested methods of producing porous materials as found in the
following United States Patents:
______________________________________
Pat. No. TITLE
______________________________________
5,137,634 Composite Membranes
5,215,943 Ceramic Membranes With Enhanced
Thermal Stability
5,227,342 Process Of Making Porous Ceramic
Materials With Controlled Porosity
______________________________________
A standard technique for making a porous metal mat is to employ filaments,
that is, small diameter wires or fibers that are assembled and pressed
together into a uniform thick mat in which the loose filaments are bonded
together. While this type of mat works very successfully in various
chemical processes, including electrolytic processes, nevertheless, such
porous metal fibrous mats are difficult to make and therefore expensive.
The present invention provides a way of making a porous metal mat
employing expanded metal foil that produces a mat having the porosity and
other features similar to a fibrous mat but wherein the costs of
production of the mat are substantially less than that of a fibrous mat.
A better understanding of the invention will be obtained from the following
description of the preferred embodiments, taken in conjunction with the
attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of a typical expanded metal foil.
FIG. 2 is a cross-sectional view as taken along the line 2--2 of FIG. 1
showing a typical cross-sectional configuration of an expanded metal foil
and showing that the thickness of the uncompressed expanded metal foil is
greater than the thickness of the foil itself.
FIG. 3 is a plan view of a flattened expanded metal foil, that is, a foil
that, after having been expanded, is flattened such as by a press or by
passing it through rollers to return the thickness of the flattened metal
foil to approximately that of the normal thickness of the foil prior to
expansion.
FIG. 4 is a cross-sectional view as taken along the line 4--4 of FIG. 3
showing a flattened expanded metal foil.
FIG. 5 is a diagrammatical illustration of stacking expanded metal foils to
form an assembly. In the preferred arrangement the foils are stacked so
that the flattened expanded metal foils have alternate positions in the
stack. The stack is preferably formed
FIG. 6 is that the openings in each layer of foil are out of register with
the openings in adjacent foil layers so that, in the stacked assembly,
few, if any, direct passageways from one surface to the other of the
finished mat exist.
FIG. 6 is a pictorial representation of a finished mat in which the stack
has been compressed and bonded into a semi-rigid electrically conductive
mat. The thickness of the mat is determined by the number of layers of
expanded metal foil employed and the amount of compression applied to the
assembly. The layers of the porous metal electrical mat of FIG. 6 are
bonded to each other either mechanically such as by stapling or riveting,
by heat, such as by welding or brazing, or preferably by diffusion
bonding.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a plan view, and FIG. 2 is a cross-sectional view of a typical
expanded metal foil. Expanded metal is well known in industry. A thin
sheet or foil of metal is perforated with slits and then stretched to
"expand" the foil. Expansion greatly increases the area of the original
foil sheet and is characterized by diamond-shaped openings formed in the
foil. In FIG. 1 the expanded foil is generally indicated by the numeral 10
and is formed by continuous filaments 12 that make up the foil after
expansion, the filaments being separated by diamond-shaped openings 14.
FIG. 2 is a cross-sectional view of a portion of the expanded metal foil as
taken along the line 2--2 of FIG. 1. In the normal procedure of expanding
metal foil the result is a foil having a thickness "T" that is greater
than the nominal thickness of metal foil before it is expanded.
FIG. 3 shows a plan view of a metal foil of the type shown in FIG. 1 but in
which the foil is flattened. The flattened expanded metal foil is
indicated by numeral 16. It retains the strands or filament 12 and the
openings 14 but, as shown in the cross-sectional view of FIG. 4, the
flattened foil has a thickness "T.sub.1 " that is approximately the
nominal thickness of the foil prior to expansion. The thickness "T.sub.1 "
is less than the thickness "T" as seen in FIG. 2. The flattened metal foil
16 as shown in FIGS. 3 and 4 can be obtained by subjecting the expanded
metal foil of FIG. 1 to a press or by passing the expanded metal foil
through rollers to flatten the foil so that it appears as in FIGS. 3 and
4.
To form a porous metal mat, successive layers of expanded metal foil are
stacked together as depicted in FIG. 5. In the preferred arrangement,
layers are alternated between expanded metal foil 10 and flattened
expanded metal foil 16. However, it is not necessary that the assembly
have an equal number of flattened and non-flattened layers of expanded
foil since the assembly could be made by placing two or more layers of
expanded foil adjacent each other followed by a single layer of flattened
foil and the relationship repeated. However, there is advantage in
stacking the layers alternately, as illustrated in FIG. 6, since this
system provides a completed porous metal mat having small dimensioned
interstices between the layers through which liquids or gases can pass and
where liquids and/or gases can be subjected to electrolytic action.
After the layers of expanded metal foil and flattened expanded metal foil
are stacked, as in FIG. 5, they are compressed together and bonded so as
to form a semi-rigid electrically conductive mat. Bonding may be
accomplished mechanically, that is, by stapling or riveting the stack
together. Another means of bonding the layers of expanded metal foil
together is by welding or brazing. A third, and a preferred embodiment,
includes diffusion bonding the stacked layers together in which, in the
usual manner of diffusion bonding, the stacked mat is placed in a furnace
with a protective atmosphere and brought to a predetermined temperature
under selected conditions that cause the layers of foil to diffusion
bonded to each other while preserving the porosity of the stacked
assembly.
In the process of stacking the layers of expanded metal foil and flattened
expanded metal foil, it is highly desirable that the layers be stacked so
that the openings 14 do not consistently align with each other. That is,
the expanded metal foil layers should be stacked so that the openings 14
are out of alignment with adjacent layers so that the mat 18 when
completed is substantially free of any openings that pass directly through
the mat from one surface to the other.
The invention has been tested by producing a mat foil formed of titanium
metal foil having a nominal thickness of about 0.004 inches. When titanium
foil of this thickness is expanded, the resultant thickness "T", as shown
in FIG. 2, is about 0.005 inches. When the expanded titanium foil is
flattened the thickness "T.sub.1 ", as shown in FIG. 4, is returned to
about 0.004 inches, that is, substantially the thickness of the foil prior
to expansion. Porous metal mats formed according to this invention can be
made of any size, depending upon the size of sheets of porous metal foil
employed in the process. The typical mats that are highly useful to
function as electrodes in the chemical industry can be from 12 inches
square up to 48 inches square. The thickness of the completed mat is
directly related to the number of layers employed, and it can be from
about 0.125 inches thick up to about 0.25 inches thick. These are by way
of examples only and not by limitations it can be seen that the process of
this invention makes it simple to control the thickness of the mat by the
number of layers of expanded metal foil employed. If the layers are
compressed prior to or during the bonding process the finished mat will
have less thickness than if the layers are not compressed extensively
during the bonding process.
The claims and the specification describe the invention presented and the
terms that are employed in the claims draw their meaning from the use of
such terms in the specification. The same terms employed in the prior art
may be broader in meaning than specifically employed herein. Whenever
there is a question between the broader definition of such terms used in
the prior art and the more specific use of the terms herein, the more
specific meaning is meant.
While the invention has been described with a certain degree of
particularity, it is manifest that many changes may be made in the details
of construction and the arrangement of components without departing from
the spirit and scope of this disclosure. It is understood that the
invention is not limited to the embodiments set forth herein for purposes
of exemplification, but is to be limited only by the scope of the attached
claim or claims, including the full range of equivalency to which each
element thereof is entitled.
Top